Consider the following linear demand function where $=$ quantity demanded, P $=$ selling price, and Y $=$ disposable income:

$$

The coefficient of P $($i$.$e$.,2\mathrm{.}1)$ indicates that $($all other things being held constant$)$:

for a one unit increase in price, quantity demanded would decline by $2\mathrm{.}1$ percent

for a one percent increase in price, quantity demanded would decline by $2\mathrm{.}1$ units

none of the above

for a one percent increase in price, quantity demanded would decline by $2\mathrm{.}1$ percent

for a one unit increase in price, quantity demanded would decline by $2\mathrm{.}1$ units